Die head with self-retiring chasers



June 21, 1955 R. STRICKLAND DIE HEAD WITH SELF-RETIRING CHASERS 6Sheets-Sheet l 7 m i I 202 1 Filed Feb. 16, 1953' June 1955 R. M.STRICKLAND 2,710,979 DIE HEAD WITH SELF-RETIRING CHASERS' I e. Sheets-S2 June 21, 1955 R, M. ASTRICKLAND 2,710,979

DIE HEAD wrm SELF-RETIRING CHASERS v Filed Feb. 16, 1953 6 Sheets-Sheet3 June 21, 1955 R. M. STRICKLAND 2,710,979

DIE HEAD WITH SELF-RETIRING CHASERS I 6 Sheets-Sheet 4 Filed Feb. 16,1953 June 21, 1955 R, M. STRICKLAND 2,710,979

DIE HEAD WITH SELF-RETIRING CHASERS Filed Feb. 16, 1953 6 Sheets-Sheet 5'II/I/Ill, I

R. M. STRICKLAND DIE HEAD WITH SELF-RETIRING CHASERS June 21, 1955 6Sheets$heet Filed Feb. 16, 1953 A EE 2,710,979 Patented June 21, 19552,710,979 I DIE HEAD WITH SELF-RETIRIN G CHASERS Royce M. Strickland,New Haven, Conn., assignor to Greenfield Tap and Die Corporation,Greenfield, Mass., a corporation of Massachusetts Application February16, 1953, Serial No. 337,011

10 Claims. (Cl. 10-96) This invention relates generally tothread-cutting tools, and more particularly to machine-operated dieheads having automatically retiring thread-cutting chasers for quickaxial retraction of the die heads from work after the same is externallythreaded.

A die head of this type is shown and described in my prior Patent No.2,557,040, dated June 12, 1951. This prior die head has a carrier inwhich a plurality of chasers are radially movable by means of cams on anoperating ring which is carried by and turnable on the carrier.

The operating ring is normally spring-urged into a retract position inwhich its cams hold the chasers retracted from the work. On turning theoperating ring into a cutting position in which the cams thereon holdthe chasers in thread-cutting position, the operating ring becomeslocked to a releasable latch to prevent its springreturn into retractposition during a thread-cutting operation of the die head. Customarily,a die head of this type performs its designated thread-cutting operationby being advanced axially over the work with its chasers inthread-cutting engagement therewith, while the work is held axiallyimmovable but is turned at a rate appropriate for the formation of thedesired thread. At the end of a thread-cutting operation, the latch ofmy prior die head is released from the operating ring to permit quickspring-return of the latter into its retract position before the diehead is axially withdrawn from the threaded work. The carrier of myprior die head also carries an axially slidable trip bar, and theaforementioned latch is a pin on a pivoted lever on a'retainer platewhich is mounted on the carrier. The latch lever is normallyspring-urged into latching position, and is actuated by the trip bar ineither one of two alternate ways to achieve automatic release of theoperating ring from the latch pin on conclusion of a thread-cuttingoperation of the die head. Thus, the trip bar may, toward the end of theaxial advance of the die head during a thread-cutting operation on work,move into engagement with a fixed stop and hold the latch lever againstfurther advance movement with the die head, whereupon the operating ringwill move out of locking engagement with the latch pin and bespring-returned to its retract position at the end of the thread-cuttingoperation; As an alternative to using a fixed stop for the tripping ofthe latch lever, the latter may be linked by the trip bar to a mountinghead which is yieldingly connected with the die head and imparts to thesame the requisite advance motion for a thread-cutting operation. Withthis arrangement, the operating ring will move out of locking engagementwith the latch pin on stopping the advance motion of the mounting headprior to the conclusion of the thread-cutting operation while the diehead is drawn further forward by virtue of the engagement of its chaserswith the thread being cut on the turning work.

While it has previously been stated that the operating ring becomeslocked to the latch pin on turning the former into its cutting position,the actual lock 15 between the latch pin and an angularly adjustablelatch on an auxiliary ring which turns with and is angularly adjustableon the operating ring, permitting thereby radial adjustment of thechasers for cutting thread on work of different diameters on angularlyadjusting the "auxiliary ring, and permitting further radial adjustmentof the chasers for rough-cutting and fine-cutting, for ininstance, onangularly adjusting the latch on the auxiliary ring. The auxiliary ringand the latch are guided for angular adjustment in an annular recess inthe operating ring, and the latch, which is an arcuate member, isretained on the auxiliary ring by having low extension lugs at its endsproject beneath releasably mounted gib plates on the auxiliary ring withsufficient lengthwise clearance to permit angular adjustment of thelatch on the auxiliary ring. The angular adjustment of the arcuate latchis are complished by manipulating a readily accessible cut-selectinghandle which has a circular hub that is fittedly received in a radialgroove in the auxiliary ring and provided with an eccentric shankpivotally received in the latch. Normally urging the operating memberinto its retract position is a compressed helical return spring whichextends arcuately in the aforementioned annular recess in the operatingring between the auxiliary ring and the aforementioned retainer plate onthe carrier. One end of this return spring bears against one of theaforementioned gibs and the other end thereof bears against a projectingpin on the retainer plate.

It is an important object of the present invention to provide a die headof this type which is of shorter length, has fewer parts, and is quickerand easier assembled and disassembled, than my aforementioned prior diehead.

Thus, it is an object of the present invention to provide the auxiliaryring with a peripheral groove with which the arcuate latch is slidablyinterlocked for its retention on the auxiliary ring, eliminating therebythe aforementioned gibs of my prior die head, and further eliminatingthe task of mounting these gibs on and removing them from the auxiliaryring, and instead accomplishing the retention of the latch on and itsrelease from the auxiliary ring by mere lateral placement of the latchinto interlock with and lateral removal from interlock with theperipheral groove of the auxiliary ring when the latter is removed fromthe annular recess in the operating ring.

It is another object of the present invention to have the hub of thecut-selecting handle fittedly received in a radial groove in the arcuatelatch and pivoted on an eccentric pin projecting from the auxiliary ringinto the groove, thereby not only providing for a rotary mount of thehandle hub with minimum strain on its pivot, but

also permitting narrower construction of the auxiliary ring and acorrespondingly shorter overall length of the present die head ascompared to that of my prior die head.

It is a further object of the present invention to provide'the auxiliaryring with a groove in which the return spring for the operating ringextends with part of its diameter, permitting thereby even narrowerconstruction of the auxiliary ring and corresponding further reductionof the overall length of the die head.

It is another object of the present invention to have one end of thereturn spring for the operating ring bear directly against an end of thearcuate latch, permitting thereby the use of a long spring which notonly has I more uniform spring characteristics throughout itsaidjustable operating range, but will also tire less over an extendedperiod of use, than the spring in my prior die head which is necessarilyshorter because it bears against a gib rather than against the latchdirectly.

A further object of the present invention is to have provisions for theinstallation of the aforementioned return spring in and its removal fromthe present die a head with much less effort and skill than is requiredfor the installation of the return spring in and its re moval from myprior die head.

Another object of the present invention is to have provisions in thepresent die head to facilitate the task of bringing the cams on theoperating ring into cooperative relation with the chasers afterinstallation of the latter in the operating ring.

It is another object of the present invention to have a structurallysimple adapter, as a substitute for the structurally more complicatedand more costly latching and tripping provisions of the present diehead, for the release of the operating ring for spring-return to itsretract position when the die head is drawn away from its mounting headby the turning work being threaded after the forward motion of themounting head has been stopped prior to the conclusion of athread-cutting operation of the die head.

Further objects and advantages will appear to those skilled in the artfrom the following, considered in conjunction with the accompanyingdrawings.

In the accompanying drawings, in which certain modes of carrying out thepresent invention are shown for illustrative purposes:

Fig. l is a side view of a die head embodying the present invention;

Fig. 2 is a front view of the same die head;

Fig. 3 is a longitudinal section through the die head, takensubstantially on the line 3-3 of Fig. 2;

Fig. 4 is a cross section through the die head, taken substantially onthe line 4-4 of Fig. 3;

Fig. 5 is a transverse section through the die head, taken substantiallyon the line 5-5 of Fig. 4;

Fig. 5A is a fragmentary section through a part of the die head;

Fig. 6 is a transverse section through the die head, taken substantiallyon the line 6-6 of Fig. 4;

Fig. 7 is a fragmentary longitudinal section through the die head, takensubstantially on the line 7-7 of Fig. 4;

Fig. 8 is a cross-section through the die head, taken on the line 8 8 ofFig. 1;

Fig. 9 is another cross-section through the die head, takensubstantially on the line 9-9 of Fig. 3;

Figs. 10, 11 and 12 are sections similar to Fig. 9 but showing certainoperating parts of the die head in different relative positions;

Fig. 13 is a cross-section through the die head, taken substantially onthe line 13-13 of Fig. 1;

Fig. 14 is a fragmentary front view of the die head .1

with the thread-cutting chasers removed therefrom;

Fig. 14A is a fragmentary section taken on the line 14A-14A of Fig. 14;

Fig. 15 is a side view of a modified die head embodying the presentinvention;

Fig. 16 is an end view of a prominent sub-assembly of the modified diehead of Fig. 15;

Fig. 17 is a section taken on the line 17-17 of Fig. 16;

Fig. 18 is a part-elevational and part-sectional view of the modifieddie head;

Fig. 19 is a fragmentary section through the subassembly of Fig. 16,indicating a mode of assembly of certain parts of the sub-assembly;

Fig. 20 is a fragmentary section taken on the line 20-20 of Fig. 18;

Fig. 21 is a section taken on the line 21-21 of Fig. 19; and

Fig. 22 is a perspective view of a certain detail element of themodified die head.

Referring to the drawings, and more particularly to Figs. 1 to 3thereof, the reference numeral 30 designates a die head having athread-cutter unit 32 and a mounting head 34 therefor. The thread-cutterunit 32 comprises a chaser carrier 36, an operating member 38, a

retainer member 40, chaser adjustment provisions 42, and automaticchaser retiring provisions 44.

The carrier 36 is cylindrical and provided at its front with an enlargedhead 46 which is centrally recessed at 48 and provided with a pluralityof equiangularly spaced radial guideways 50 for thread-cutting chasers52. In the present instance, there are four guideways 50 for fourchasers 52. The carrier head 46 is in its rear provided with an annularrecess 54 which intersects the guideways St The carrier 36 is at itsrear provided with a cylindrical shank 56 for the reception of theretainer member 40.

The operating member 38 is in the form of a ring which is journalled onthe carrier 36 (Figs. 3 and 13) and is held with its front face 60against the adjacent rear face 62 of the carrier head 46 in a mannerdescribed hereinafter. Projecting forwardly from the front face 60 ofthe operating ring 38 and into the annular recess 54 in the carrier head46 are four identical equiangularly spaced cam lugs 64 (Figs. 2, 3 and5) which are normally received in transverse grooves 66 in the rearfaces 63 of the chasers 52 in the adjacent guideways 50 (Fig. 6). Thecam lugs 64 serve to move the chasers 52 in their guideways 59 inwardlyinto thread-cutting engagement with work and outwardly from cuttingengagement with work on turning the operating ring 38 counterclockwiseand clockwise, respectively, as viewed in Fig. 2, within a normaloperating range to be described.

The carrier 36 is in its periphery provided with a groove 70 (Fig. 13)the angular extent of which defines the aforementioned normal operatingrange of the ring 38 within which the latter may be turned for movingthe chasers 52 into and out of thread-cutting engagement with work. Theperipheral groove 70 in the carrier 36 is substantially semi-circular incross-section (Fig. 3) for the normal fitted reception of substantiallyonehalf of a steel ball 72 which is also normally received in across-sectionally part-circular groove 74 in a plunger 76 in theoperating ring 38 to prevent axial movement of the ring 38 on thecarrier 36 and permit rotation of the former on the latter within theaforementioned operating range defined by the peripheral extent of thegroove '70 in the carrier. The plunger '76 is slidably received in anaperture 78 in the operating ring 38 and is normally urged by a spring80 into the ball-locking position shown in Fig. 13 in which one end of aperipheral groove 82 in the plunger bears against a stop pin 84 in theoperating ring. In order to release the ball 72 from interlock with thegroove 70 in the carrier 36, to permit axial removal of the operatingring 33 from the latter or to permit rotation of the operating ring onthe carrier outside its normal operating range for purposes hereinafterdescribed, the plunger 76 is deprcssed to bring a groove 86 with apreferably part-spherical bottom 88 in the plunger into registry withthe ball 72. The groove 86 in the plunger 76 is sufficiently deep toaccommodate the entire ball 72 and thus release the operating ring fromthe carrier. The opening 89 in the operating ring through which the ball72 normally projects is of slightly smaller diameter than the ball, sothat the latter is retained in the aperture 78 even when the operatingring is removed from the carrier.

The chaser adjustment provisions 42 comprise an auxiliary or adjustmentring 90 and a latch 92 (Figs. 4, 6 and 9), of which the ring 90 servesfor the radial adjustment of the chasers 52 for cutting thread on workof different diameters, and the latch 92 serves for radial adjustment ofthe chasers 52 for selective rough,

" medium and fine cutting performance by the same, all as more fullydescribed hereinafter. The auxiliary ring 90 is turnable in an annularrecess 94 in the rear end of the operating ring 38 (Figs. 3 to 7) andrests against the bottom 96 of the recess 94. Projecting from theauxiliary ring 90 into an arcuate groove 98 in the bottom 96 of theannular recess 94 in the operating ring 38 is an adjustment stud 100(Figs. 3 and 13) which is engaged on opposite sides by adjusting screws102 and 104 that are threadedly received in the operating ring 38. Theauxiliary ring is thus angularly adjustably coupled to the operatingring 38 by the stud and the screws 102 and 104, and angular adjustmentof the auxiliary ring 90 relative to the operating ring 38 isaccomplished by simple adjustment of the screws 102 and 104 which arereadily accessible from the outside of the die head.

The auxiliary ring 90 is provided with a diametrically reducedcylindrical extension 106 which, as shown in Fig. 6, extends to the rearend of the operating ring 38. The ring extension 106, which isinterrupted or cut-away at 108 and 110 (Figs. 4, 9 and 10) for purposeswhich will appear obvious hereinafter, leaves in the annular recess 94 aring-like space 112 a length of which is occupied by the arcuate latch92. For its retention on the auxiliary ring 90 and its guidance in anarcuate path into diiferent positions of angular adjustment on theauxiliary ring, the latch 92 is received with a sliding fit between theannular wall 114 of the operating ring 38 and the ring extension 106 andis interlocked over the'greater part of its length with a lateral guiderib formation 1-16on the ring extension 106. The guide rib formation 116extends from the cut-away 108 in the ring extension 106 approximately tothe place indicated at 118 in Fig. 4, and from there extends part-wayaround the ring extension 106 as a canted lip 120 of the cross-sectionshown in Fig. 3, for instance. While the rib formation 116 on the ringextension 106 securely retains the latch 92 on the auxiliary ring 90when the latter is installed in the annular recess 94 in the operatingring 38, the latch 92 may readily be laterally removed from theauxiliary ring when the latter is removed from the annular recess 94 inthe operating ring.

The latch 92 is angularly adjustably coupled to the auxiliary ring 90.To this end, the face 122 of the latch next to the auxiliary ring 90(Fig. 6) is provided with a radial groove 124 (Figs. 5 and 9) for thefitted reception of the circular hub 126 of a cut-selecting handle orlever 128 which for ready manipulation extends through a peripheral slot130 in the operating ring 38 to the outside of the latter. Projectingfrom the auxiliary ring 90 into the radial groove 124 in the latch 92 isa pin 132 (Figs. 5 and 9) which serves as an eccentric pivot for the hub126 of the cut-selecting lever 128. Accordingly, on turning thecut-selecting lever 128 into different angular positions, the latch 92will be angularly adjusted relative to the auxiliary ring 90. Provisionsare also made for yieldingly arresting the cut-selecting lever 128 in aplurality of most frequently used cutselecting positions, in thisinstance three positions for rough, medium and finish cuts. To this end,the face of the hub 126 of the lever 128 which is adjacent the auxiliaryring 90 is provided with three equiangularly spaced depressions 134(Fig. 9) any one of which may be engaged by a spring-urged ball-typedetent or plunger 136 in the auxiliary ring.

The chasers 52 are normally yieldingly retracted from work by means ofan axially compressed helical retract or return spring 140 which extendsarcuately in a part of the aforementioned ring-like space 112 and isretained therein by the canted lip 120 on the auxiliary ring 90 (Figs. 3and 4). The return spring 140 bears with one end against the end 142 ofthe latch 92, and with its other end against a pin 144 which projectsfrom the previously mentioned retainer member 40 into the ringlike space112. The retainer member 40 is in the form of a ring which bears againsta shoulder 146 on the carrier 36 and is removably mounted thereon bybolts 148 (Fig. 7). The retainer member or ring 40 not only holds theauxiliary ring 90 and latch 92 in the annular recess 94 in the operatingring 38, but also holds the operating ring 38 against axial removal fromthe carrier 36 even when the hereinbefore described plunger 76 isdepressed. When the retainer ring 40 is mounted on the carrier 36 asdescribed, the spring-backing pin 144 thereon will be located in theposition shown in Figs. 4 and 11 in which it will hold the return spring140 axially compressed even when the same is lengthwise expanded to itsmaximum extent during normal use of the die head, i. e., when theoperating ring 38 and the adjustable parts 90 and 92 thereon are in theretract position shown in Fig. 11 in which the chasers 52 are retiredfrom work. Rotation of the operating ring 38 and parts carried therebybeyond the retract position (Fig. 11) under the urgency of thecompressed return spring 140 is prevented by the ball 72 which thenbears against the left end of the peripheral groove 70 in the carrier 36as viewed in Fig. 13.

In order to advance the chasers 52 radially inwardly into thread-cuttingengagement with work, the operating ring 38 is, by means of a readilyaccessible operating or resetting handle 156 thereon, turned against thecompression of the return spring 140, clockwise as viewed in Fig. 11,into the cutting position shown in Figs. 4 and 9 in which the latch 92becomes locked to a yielding latch pin 158 on the retainer ring 40.Clockwise rotation of the operating ring 38 from the retract position inFig. 11 to the cutting position in Fig. 4 will appear ascounterclockwise rotation of the operating ring as viewed in Fig. 2, andit will be readily observed in the latter figure that suchcounterclockwise rotation of the operating ring will indeed cause thecam lugs 64 thereon to move the chasers 52 inwardly in their guideways50. Inasmuch as the compression of the return spring 140 is quiteconsiderable when the operating ring 30 is in its cutting position (Fig.4), the latch 92 is preferably provided with a hardened steel plate 160which locks with the latch pin 158 and shows little wear even afterlong,

use. Further, to prevent rapid wear of the mounting bolts 148 of theretainer ring 40 and their subjection to excessive shearing stresseswhen the latch pin 158 is, through intermediation of thelocked latch 92(Fig. 4), subjected to the considerable compression of the return spring140, the retainer ring 40 is coupled to carrier 36 so that the mountingbolts 148 serve merely to hold the retainer ring against the shoulder146 on the carrier (Fig. 7 The coupling between the retainer ring 40 andthe carrier 36 comprises opposite coupling ribs 162 on the retainer ring40 having opposing machined surfaces 164 which are in couplingengagement with opposite machined surfaces 166 of a central coupling rib168 on the carrier 36 (Figs. 3, 4 and 9). The end of the coupling rib168 on the carrier constitutes the shoulder 146 against which theretainer ring 40 is held by the mounting bolts 148 (Figs. 4 and 7).

After a concluded thread-cutting operation of the chasers 52, theoperating ring 38 is released for spring return from the cuttingposition in Fig. 4 into the retract position shown in Fig. 11 onwithdrawing the latch pin 158 from locking engagement witth the latch92. The latch pin 158 is carried by a latch lever 170 which is mountedfor pivotal movement on the retainer ring 40 (Fig. 3). The latch pin 158has a threaded shank 172 which extends through the latch lever 170 andreceives a nut 174. Preferably, the nut 174 is sufiiciently tightenedagainst a spring washer 175 to mount the latch pin 158 securely on thelatch lever 170, yet permit slight rotation of the latch pin on thelatch lever so that the former may be self-positioning for even surfaceengagement with the latch 92 with a minimum of wear to the latch pin. Inorder to limit rotatability of the presently square latch pin 158, thesame projects into a somewhat wider transverse groove 176 in the latchlever 170 (Figs. 3 and 8). The latch lever 170 itself is removablymounted in a radial groove 178 in the retainer ring 40 (Figs.3 and 8) bymeans of a spring-urged plunger 180 which is received in aligned notches182 and 184 in the latch lever 170 and retainer ring 40, respectively,and extends into a recess 186 in the carrier 36. The plunger 180 is atone end provided with a frusto-conical head 188 which is seated in acorrespondingly shaped socket-like portion 190 of the notch 182 in thelatch lever 170. Surrounding that part of the plunger 180 which extendsinto the recess 186 in the carrier 36, and interposed between theretainer ring 140 and a head 194 on the other end of the plunger 180, isa compression-type spring 192 which, through intermediation of theplunger 180, draws the latch lever 170 fully into its reception groove178, i. e., into the position shown in Fig. 3 in which the latch leverand its latch pin 158 are in latching position. Accordingly, thespring-urged plunger 180 not only holds the latch lever 170 yieldinglyin its latching position, but acts also as a pivot for the latch lever,as will be readily understood. Moreover, the latch lever 170 is readilyassembled with or disassembled from the retainer ring 40 when the latteris dismounted from the carrier 36, by

simply laterally inserting the spring-urged plunger 180 .2

into or laterally removing the same from the aligned notches 182 and 184in the latch lever 170 and retainer ring 40.

The mounting head 34 comprises, in the present instance, two parts 200and 202 (Figs. 1 and 3) having head flanges 204 and 206, respectively,which are secured to each other by means of bolts 208 the heads 210 ofwhich are preferably received in recesses 212 in the flange 204 of thepart 200 (Fig. 6). The part 200 is provided with a forwardly extendingcylindrical shank 214 on I! which the carrier 36 is mounted for slidingmovement. The other part 202 of the mounting head 34 has a rearwardlyextending shank 216 which may be mounted in the turret of a screwmachine or in any other suitable holder. The flange 204 of the part 200of the mounting head is also provided with a lug extension 218 which isapertured at 220 for the extension therethrough with clearance of a partof a tripping device 224 to be described.

For a reason which will become evident hereinafter,

the thread cutter unit 32 is operatively connected with the mountinghead 34 to permit limited yielding forward movement of the formerrelative to the mounting head 34. To this end, there are provided twodiametrically opposite spring-urged plungers 230 (Fig. 5) each of Jwhich is laterally rcrnovably received in aligned notches 232 and 234 inthe retaining ring 40 and extends into a recess 236 in the carrier 36.Each of the plungers 230 extends also beyond the retainer ring 40 and isprovided at its outer end with an enlarged head 238 which groove 240 inthe head 238 of each plunger 230 for releasably connecting the latterwith the mounting head. Surrounding a major length of each plunger 230and interposed between an end head 248 thereof and a shoulder 250between the notches 232 and 234 in the retainer member 40 is an axiallycompressed retraction spring 252. It follows from Fig. 5 that thespring-urged plungers 230, removably mounted as described, will tend toyieldingly retract the thread cutter unit 32 toward the mounting head 34if the former is moved forwardly in the direction of the arrow 254 (Fig.5) relative to the mounting head 34.

The thread cutter unit 32 is, despite the tendency of the spring-urgedplungers 230 to draw the same into abutting engagement with the mountinghead 34, normally held in spaced relation with the latter by means ofdiametrically opposite spring-urged plungers 260 (Fig. 6) which areslidably received in the retainer ring 40 and have heads 26?. thatproject into recesses 264 in the carrier 36. Also received in therecesses 264 and interposed between the bottoms of the latter and theplunger heads 262 are compression-type springs 266 which overpower theretraction springs 252 of the plungers 230 (Fig. 5) and normally urgethe plunger heads 262 into engagement with the retainer ring 40 so thatthe plungers 260 will normally yieldingly hold the thread cutter unit 32spaced from the mounting head 34 to the extent indicated in Figs. 5 and6.

Inasmuch as the die head is for a conventional threadcutting performancemoved axially at a rate required for the formation of a desired thread,but is not rotated, and since the work being threaded is turned for theformationof the thread thereon by the advancing chasers of the die head,provisions are made to hold the thread cutter unit 32 against rotationon the mounting head 34 which is non-rotatably held in the turret of ascrew machine or other holder, as previously mentioned. To this end, theretainer ring 40 carries two diametrically opposite coupling pins 270(Figs. 5A and 8) each of which is slidably received in a bushing 272 inthe part 200 of the mounting head 34 and projects into a clearance hole274 in the other part 202 of the mounting head.

The previously mentioned tripping device 224 (Fig. 3) comprises atripping bar 276 which is axially slidable in a bracket 278 on thecarrier 36 and has its forward end formed as a tripping head 280. Thebracket 278 is fittingly received in a recess 277 in the carrier 36 andis removably mounted therein by a screw 279 (Figs. 2 and 3). Threadedlyreceived in the rear end of the tripping bar 276 is a stud 282 having ahead 284 which is provided with an elongated slot 286 and a hole 288that extends transversely of the slot 286. The head 284 on the stud 282extends with clearance through the aperture 220 in the lug extension 218on the part 200 of the mounting head 34. A nut 290 serves to lock thestud 282 to the tripping bar 276 in any adjusted position therein.Threadedly received on the stud 282 is a tripping member 292 having adisc portion 294 for engagement with opposite curved projections 296 onthe latch lever 170 (Figs. 1 and 3). The tripping member 292 is alsoprovided with a hexagonal head 298 for its ready axial adjustment on thestud 282 by means of a wrench or other convenient tool. Removablyreceived in a hole 300 in the lug extension 218 on the part 200 of themounting head 34 is a coupling pin 302 which extends through theaperture 220 in the lug extension 218.

The tripping device 224 may be used in either of two alternative waysfor the automatic release of the locked operating ring 38 in its cuttingposition for spring-return to its retract position at the end of athread-cutting performance of the die head. With the removable couplingpin 302 extending through the elongated slot 286 in the head 284 of thestud 282 of the tripping device as shown in Figs. 1 and 3, the latter isadapted for cooperation with a fixed stop (not shown) to bring about theretraction of the latch pin 158 from locking engagement with the latch92 at the end of a thread-cutting performance of the die head. Thus, thetripping head 280 of the tripping bar 276 will, during the forward oradvance motion of the die head during a thread-cutting operation andjust prior to the conclusion of the latter, engage a fixed stop and beheld thereby against further advance movement with the die head. Sincethe disc portion 294 of the tripping member 292 is then in engagementwith the curved projections 296 on the latch lever 170 (Fig. 3),

the latter will also be held against further advance movement with thedie head, with the result that the latch lever 170 and its pin 158 willsoon be rocked out of latching position and release the latch 92 forspringreturn of the operating member 38 into its retract position. Inorder that the latch lever 170 may thus be rocked without interferencefrom the nearby mounting head 34, the head flange 204 of the part 200thereof is recessed at 306 to provide clearance for the mounting 5 nut174 of the latch pin 158 (Fig. 3). Of course, threads 9. of variablelengths may be cut by the die head with the arrangement of the trippingdevice 224 as shown in Fig. 3, by simply adjusting the stud 282 in thetripping bar 276, or the tripping member 292 on the stud 282, or both.

As an alternative to the above-described use of the tripping device witha fixed stop, the tripping device may be linked to the latch lever 170and to the lug extension 218 on the mounting head 34. To this end, thecoupling pin 302 is temporarily removed and the tripping device 224 isturned 90 degrees from the position shown in Fig. 3 to bring the hole288 in the head 284 on the stud 282 into axial alignment with the hole300 in the lug extension 218 on the mounting head 34, whereupon the pin302 is inserted into the aligned holes 288 and 300 for coupling thetripping device to the mounting head. With this arrangement of thetripping device, the length of the latter which links the latch lever170 with the mounting head 34 will trip the latch lever and cause it torock from latching position when the forward motion of the mounting head34 is stopped while the thread-cutter unit 32 continues its forwardmotion by virtue of the engagement of the chasers 52 with the work beingthreaded. As soon as the operating ring 38 is released for spring-returnto its retract position, the spring-urged plungers 230 (Fig. 5) willretract the cutter unit 32 into its normal axial disposition on theforward shank 214 of the mounting head 34.

While the operating ring 38 is in its retract position (Fig. 11) thelatch pin 158 rests against the adjacent face 312 of the latch 92 (Fig.4), and the latch pin is ready to snap into locking engagement with thelatch 92 on turning the operating ring 38 into its cutting position, aswill be readily understood.

Angular adjustment of the auxiliary ring 90 relative to the operatingring 38 by means of the adjusting screws 102 and 104 (Fig. 13) willresult in radial adjustment of the chasers 52 for cutting thread on workof different diameters. This Will be more readily understood by assumingthat the latch 92 is locked to the latch pin 158 (Fig. 4) when theauxiliary ring 90 is being angularly adjusted. Thus, the operating ring38 and the parts 90 and 92 thereon are spring-urged against the latchpin 158, and any angular adjustment of the auxiliary ring 90 relative tothe operating ring 38 will inevitably result in relative rotationbetween the latter and the carrier and, consequently, in like relativerotation between the cam lugs 64 on the operating member and the chasers52 in the carrier (Fig. 2). Of course, the same radial adjustment of thechasers for cutting thread on work of different diameters is achieved byangularly adjusting the auxiliary ring 90 on the operating member whilethe latter is in its retract position.

Angular adjustment of the latch 92 on the auxiliary ring 90 by means ofthe cut-selecting lever 128 will result in further radial adjustment ofthe chasers 52 in the carrier 36. This will also be more readilyunderstood by assuming that the latch 92 is locked to the latch pin 158(Fig. 4) when the latch is being angularly adjusted on the auxiliaryring 90. Thus, the operating ring 38 and the auxiliary ring 90 and latch92 thereon are spring-urged against the latch pin 158, and any angularadjustment of the latch 92 relative to the auxiliary ring willinevitably result in relative rotation between the operating ring 38 andthe carrier 36 and, consequently,

in like relative rotation between the cam lugs 64 on the operatingmember and the chasers 52 in the carrier issu ning that the latch 92 islocked to the latch pin 158, the hub 126 of the cut-selecting lever 128will, on turning the latter from the position shown in Fig. 9 to thatshown in Fig. and by the action of the eccentric pivot 132, turn theauxiliary ring 90 and coupled operating ring 38 slightly clockwise asviewed in Fig. 10, resulting in equal turning movement of the.

- purposes, are eliminated.

cam lugs 64 in counterclockwise direction, however, as viewed in Fig. 2,and hence, in slight radial inward movement of the chasers 52.Accordingly, rotation of the cut-selecting lever 128 from the positionin Fig. 9

. to the position in Fig. 10 will result in slight radial inward motionof the chasers 52 for a rough cut by the same. Conversely, rotation ofthe cut-selecting lever 128 from the position in Fig. 10 to the positionin Fig. 9 will result in slight radial outward motion of the chasers 52for a fine cut by the same. A medium cut by the chasers 52 is achievedby turning the cut-selecting lever 128 into a position intermediatethose shown in Figs. 9 and 10.

If desired, a thread may first be formed on work with a rough cut byturning the cut-selecting lever 128 into the rough-cut position shown inFig. 10. After the thread is roughed in the work, the thread may befinishcut by turning the cut-selecting lever 128 into the fine-cutposition in Fig. 9. At the end of the fine-cut performance of thechasers 52 on the work, the operating ring 38 will be spring-returned toits retract position and the inertia then imparted to the cut-selectinglever 128 will jar the same from its fine-cut position (Fig. 9) andthrow it into its rough-cut position (Fig. 10), ready for the initialrough cut on the next work to be threaded.

The instant die head is, in comparison to my aforementioned prior diehead, simpler in construction, of shorter overall length, and easier toassemble or disassemble. Thus, by slidably interlocking the latch 92directly with the ring extension 106 on the auxiliary ring 90, asdescribed, the gibs used heretofore for the retention of the latch onthe auxiliary ring and the task of mounting these gibs on anddismounting them from the auxiliary ring for latch assembly anddisassembly In slidably interlocking the latch 92 with the auxiliaryring 90, as described, the return spring 140 for the operating ring 38may be made longer than heretofore, securing thereby the advantage thatthe spring will have more uniform spring characteristics throughout itsadjustable operating range and will tire less over an extended period ofuse. The overall length of the present die head is reduced from that ofmy aforementioned prior die head by providing the radial groove 124 forthe reception of the hub of the cut-selecting lever 128 in the latch 92,rather than in the auxiliary ring as heretofore. The overall length ofthe present die head is further reduced by a further reduction of thewidth of the auxiliary ring and latch assembly which is accomplished byproviding the auxiliary ring 38 with an arcuate groove 320 in which 'thereturn spring 140 extends with part of its diameter (Figs. 3 to 6).Further, the mounting of the hub of the cut-selecting lever 128 on theeccentric pin 132, which is, in turn, mounted in the auxiliary ring 90,saves the eccentric pin from undue strain and wear from the hub 'of thecut-selecting lever.

ring-like space 112 defined by the auxiliary ring 90 in the annularrecess 94 in the operating ring 38 (Fig. 4), and underneath the cantedlip on the ring extension 106 without interference from thespring-backing pin 144 on the retainer ring 40. However, the thennon-compressed return spring thus placed in the die head will, even whenbearing against the end 142 of the latch 92 (Fig. 4), be in the way, andprevent the entry into the ring-like space 112, of the spring-backingpin 144 when the retainer ring 40 is re-mounted on the carrier 36. Ac-

cordingly, the non-compressed return spring 140 will have to be movedout of the way of the spring-backing pin 144 on the retainer ring inorder to permit the reas= sembly of the latter with the rest of thethread-cutter unit' 32. To this end, the spring-urged plunger 76 isdepressed to release the operating ring 38 for rotation on the carrier36 outside of its normal operating range, whereupon the operating ring38 and the parts 90 and 92 carried thereby are turned counterclockwisefrom the position in Fig. 4 into a position like or similar to thatshown in Fig. 12. In the course of such out-of-normal-range rotation ofthe operating ring 38 and the parts 90 and 92 thereon into the positionshown in Fig. 12, the auxiliary spring retainer pin 322 will engage theadjacent end of the return spring 140 and move the same out of theregion in the ring-like space 112 into which the spring bac'king pin 144on the retainer ring 40 will normally project when the latter isre-mounted on the carrier 36 (Fig. 12). After remounting the retainerring 40 on the carrier 36, the operating ring 38 and the parts 90 and 92thereon are returned to their normal operating range on the carrier byclockwise rotation of the operating ring as viewed in Fig. 12 into itsnormal retract position (Fig. 11) in which the ball 72 is againinterlocked with the left end of the peripheral groove 70 in the carrier(Fig. 13). During this return rotation of the operating ring 38 from theposition shown in Fig. 12 into the normal retract position shown in Fig.11, the return spring 140 will follow the auxiliary spring-retainer pin322 until the latter passes the spring-backing pin 144, whereupon thereturn spring will bear against the latter and become axially compressedthereby, during the remainder of this return rotation of the operatingring, to the extent required for normally urging the latter into itsretract position.

For initial assembly of the chasers 52, or their reassembly aftersharpening, with the carrier 36, or for replacement of a chaser 0rchasers, the spring-urged plunger 76 is depressed to release theoperating ring 38 for rotation on the carrier 36 outside its normaloperating range into a position like or similar to that shown in Fig. 14in which the cam lugs 64 on the operating ring are fully retracted fromthe guideways in the carrier 36. The chasers 52 may thereupon beradially inserted in the guideways 50. In order to facilitate the entryof the cam lugs 64 into the tranverse grooves 66 in the rear of theinserted chasers 52 on returning the operating ring 38 to its normaloperating range on the carrier 36, there are provided in the front faceof the operating ring 38 four pairs of spring-urged detents 330, onepair for each chaser, which are exposed to the guideways 50 when theoperating ring is turned to the out-of-normal-range posi* tion shown inFig. 14. Each of these detents 330 is in this instance a steel ball(Fig. 14A) retained in a cage 332 in the carrier and normally urged by acompressiontype spring 334 to project slightly forward of the front face60 of the carrier. The spring-urged balls or detents 330 of each pairare spaced radially from each other to such an extent that they willyieldingly engage the opposite side walls of the transverse groove 66 inthe adjacent inserted chaser 52 and thus yieldingly hold the latter withits transverse groove 66 in alignment with the adjacent cam lug 64 whichwill move into registry with the groove 66 on returning the operatingring from the chaser-inserting position shown in Fig. 14 into its normaloperating range on the carrier 36.

The operating ring 38 is also provided with a stop pin 336 (Figs. 7 and12) which projects through a periphcral notch 333 in the auxiliary ring90 into the ring-like space 112 and engages the spring-backing pin 144on the retainer ring 40 when the operating ring 38 is turned into thechaser-inserting position shown in Fig. 14 in which the pairs ofspring-urged detents 330 are fully exposed in the guideways 50 in thecarrier 36. To accomplish engagement of the stop pin 336 with thespring-backing pin 144 for full exposure of the spring-urged detents 330in the guideways 50, it may be necessary to change the angularadjustment of the auxiliary ring on the op erating ring 38.

Reference is now had to Figs. 15 and 18 which show a modified die head30. More particularly, the modified die head 30' is in all respects likethe hereinbefore described die head 30, except that the retainer ring40, the latch lever 170, the tripping device 224 and the mounting head34 of this previously described die head 30 have been replaced by astructurally much simpler and less costly adapter 340. The adapter 340comprises two main parts 342 and 344 (Figs. 16 and 17) of which the part342 takes the place of the previously described retainer ring 40,. andis received on the rearwardly extending shank 56 on the carrier 36 (Fig.18) and mounted on the latter by the same bolts 148. Like the previouslydescribed retainer ring 40, the part 342 has in its front face 346opposite coupling ribs 348 and 350 which in the mounted condition of thepart 342 are in coupling engagement with the central coupling rib 168 atthe rear end of the carrier 36 (Fig. 4). The part 344 of the adapter 340takes the place of the previously described mounting head 34 and isprovided with a head flange 352 and a rearwardly extending shank 354which is mounted in the turret of a screw machine or any other holder.The part 344 is normally yieldingly drawn with its flange 352 into anannular recess 356 in the rear of the head flange 358 of the part 342 bymeans of two diametrically opposite spring-urged plungers 360 which arelaterally removably received in notches 362 in the flange 358 of thepart 342.

One end of each plunger 360 carries a head 364 which is provided with aV-shaped peripheral groove 366 and is slidably received in an aperture368 in the flange 352 of the part 344 (Fig. 17). Each plunger 360 isreleasably connected with the part 344 of the adapter by a set screw 370the conical tip 372 of which is received in the V- shaped peripheralgroove 366 in the head 364 of the plunger. Surrounding the plungers 360and interposed between heads 374 thereon and the flange 358 of the part342 are compression-type springs 376 which, through intermediation ofthe plungers 360, yieldingly draw the flange 352 of the part 344 of theadapter into the annular recess 356 in the flange 358 of the part 342.in the mounted condition of the adapter 340, the plungers 368 projectinto the recesses 236 in the carrier 36 (Fig. 5). The plungers 360 carrytransverse pins 377 which on engagement with the part 342 limit furtheryielding separation of the parts 342 and 344. When the adapter 340 isrnounted, a pin 144' (Fig. 16) on the retainer part 342 projects intothe ring-like space 112 in lieu of the previously describedspring-backing pin 144 (Fig. 4) and holds the return spring 144 inaxially compressed condition.

The part 342 of the adapter 340, which is directly mounted on thecarrier 36 of the thread-cutter unit 32',

is further coupledto the part 344 of the adapter by coupling studs 380(Fig. 16) which are slidably received in bushed apertures (not shown) inthe flange 352 of the part 344 of the adapter.

Mounted in aligned apertures 380 and 382 in the flanges 358 and 352 ofthe parts 342 and 344 of the adapter 340 is a bushing 384 (Figs. l8 and19) for sliding reception of a latch pin 158', having a shank 386extending into a peripheral notch 388 in the flange 352 of the part 344.Surrounding the shank 386 of the latch pin 158' and interposed in thebushing 384 between the bottom 392 thereof and the latch pin 158 is acompression-type spring 394 which normally urges the latch pin into thelatching position shown in Fig. 18 in which a releasahly interlocked key396 on the shank 386 of the latch pinbears against the bottom 398 of theperipheral notch 388 in the flange 352 of the part 344.

in operation of the modified die head 30', the same is advanced over theturning work being threaded the same as the previously described diehead 30. Toward the end of a thread'cutting performance of the modifieddie head, the mounting part 344 of the adapter 340 is stopped while thethread-cutter unit 32' and the retainer part 342 of the adapter 340continue to move forwardly by engagement of the chasers with the workbeing threaded, with the result that the key 396 holds the latch pin158' against further forward movement with the threadcutter unit 32' andthe latch 92 of the latter will soon be released from locking engagementwith the latch pin 153' and permit spring-return of the operating ring38 into its retract position. As soon as the chasers are retracted fromthe work, the spring-urged plungers 360 will retract the yieldinglyadvanced thread-cutter unit 32 with the retainer part 342 of the adapter340 into engagement with the mounting part 344 of the adapter, as willbe readily understood.

Since the mounting screws 148 for the retainer part 342 of the adapter340 are not accessible without first removing the mounting part 344 ofthe adapter, and since the key 396 prevents removal of the mounting part344 of the adapter from its retainer part 342 even after releasing theset screws 370 from the heads 364 of the spring-urged plungers 360 (Fig.17), it is, for the removal of the thread-cutter unit 32' from theadapter 348, necessary to first release the key 396 from interlock withthe shank 386 of the latch pin 158. This is accomplished with the aid ofa split ring 400 which is locked in a peripheral groove in the shank 386of the latch pin 158' directly beneath the key 396 which is normallyinter-' locked with the shank 386 by having a straight portion 4% of aslot interlocked with intermediate opposite fiats 464 on the shank 386(Figs. 18 and 20). For the removal of the key 396 from interlock withthe shank 386 of the latch pin 158', the shank 386 together with the key396 thereon are lifted in any convenient manner against the compressionof the spring 394 into a position like or similar to that shown in Fig.19 in which the tip 406 of a screw driver, for instance, may be appliedto the ring 409 to hold the shank 386 with the key 396 thereon outsidethe confines of the peripheral notch 388 in the flange 352 of theadapter part 344 to permit lateral outward motion of the key out ofinterlock with the flats 49-4 on the shank and into the position shownin Fig. 21 in which a circular portion 408 of the slot in the keysurrounds the shank 386 and permits removal of the key from the shankaxially thereof. In mounting the threadcutter unit 32' on the adapter340, the part 342 of the latter is first assembled with thethread-cutter unit, whereupon the part 342 of the adapter is assembledwith the mounted part 344 thereof by locking the heads 364 of thespring-urged plungers 360 to the set screws 370 and interlocking the key396 with the shank 386 of the latch pin 158 in a manner which is obviousfrom the foregoing description of the release of the key from the shankof the latch pin.

Since the modified die head of Figs. 15 and 18 dispenses with thepreviously described tripping device 224, including the bracket 278thereof, the recess 277 in the carrier.

36 (Figs. 2 and 3) is closed by a filler piece 410 (Figs. 15 and 22)which is retained in the recess 277 by the same screw 279.

The invention may be carried out in other specific ways than thoseherein set forth without departing from the spirit and essentialcharacteristics of the invention, and the present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive, and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein.

What is claimed is:

1. In a die head having a carrier with substantially eral groove forcircular guidance of said latch in said.

recess and its retention on said auxiliary member; an angularlyadjustable coupling between said latch and auxiliary member; aprojection on said carrier extending into said recess; and a compressedhelical spring extending circularly in said recess and being interposedbetween said projection and one end of said latch, said spring normallyurging said operating member into a retract position in which saidchasers are disengaged from work, the other end of said latch becominglocked to said latch pin on turning said operating member into anoperative position in which said chasers are in thread-cuttingengagement with work.

2. The combination in a die head as set forth in claim 1, in which saidarcuate latch has in one face thereof a radial groove, and said couplingcomprises an operating lever projecting to the outside of said operatingmember and having a circular hub fittedly received in said groove in thelatch, and a pin projecting from said auxiliary member and serving as aneccentric pivot for said hub.

3. In a die head having a carrier with substantially radial guidewaysfor thread-cutting chasers, the combination of an operating memberturnable on said carrier and having an annular recess in one end, ashoulder and angularly spaced first and second projections extendingwithin the confines of said recess toward said one end of the member,and cams for moving said guided chasers on turning said members; aretainer element removably mounted on said carrier adjacent said one endof the operating member and having a projection extending into saidrecess in the latter; cooperating means on said carrier and operatingmember normally limiting rotation of the latter on the former to acertain operating range of a partial revolution, and operable to releasesaid operating member for rotation outside said operating range, saidsecond projection on said operating member being arranged to pass saidprojection on said retainer element on rotation of said operating memberon said carrier outside said operating range; a releasable latch on saidretainer element; and a compressed helical spring extending circularlyin said recess and held therein by said retainer element, said springnormally bearing with one end against said first projection on saidoperating member and with its other end against the projection on saidretainer element so as normally to urge said operating member withinsaid operating range into an end position in which said chasers aredisengaged from work, said shoulder on said operating member becominglocked to said latch on turning said operating member within saidoperating range into an operative position in which said chasers are inthread-cutting engagement with work, and said second projection on saidoperating member engaging said other end of said spring and holding thelatter out of that region in said recess in the operating member intowhich said projection on said retainer element will extend on mountingthe latter on said carrier while said carrier and operating memberassume an angular relative position outside said operating range.

4. In a die head having a carrier with substantially radial guidewaysfor thread-cutting chasers, an operating member turnable on said carrierand having an annular recess in one end and cams for moving said guidedchasers on turning said member, a retainer element removably mounted onsaid carrier adjacent said one end of the operating member and having aprojection extending into said recess, cooperating means on said carrierand operating member normally limiting rotation of the latter on theformer to a certain operating range of a partial revolution, andoperable to release said operating member for rotation outside saidoperating range, and a releasable latch pin on said retainer element,the com bination of an auxiliary member turnable in said recess in theoperating member and angularly adjustably coupled to the latter forrotation therewith, said auxiliary member having a shoulder andangularly spaced first and second lateral projections extending withinthe confines of said recess toward said one end of the operating member,said second projection being arranged to pass the projection on saidretainer element on rotation of said operating member on said carrieroutside said operating range; and a compressed helical spring extend ingcircularly in said recess and held therein by said retainer element,said spring normally bearing with one end against said first projectionon said auxiliary member and with its other end against the projectionon said retainer element so as normally to urge said operating memberwithin said operating range into an end position in which said chasersare disengaged from work, said shoulder on said auxiliary memberbecoming locked to said latch pin on turning said operating memberwithin said operating range into an operative position in which saidchasers are in thread-cutting engagement with work, and said secondprojection on said auxiliary member engaging said other end of saidspring and holding the latter out of that region of said recess in theoperating member into which said projection on said retainer elementwill extend on mounting the latter on said carrier while said carrierand operating member assume an angular relative position outside saidoperating range.

5. The combination in a die head as set forth in claim 4, furthercomprising a latch angularly adjustably coupled to said auxiliary memberfor rotation therewith, one end of said latch constituting said firstprojection and the other end of said latch constituting said shoulder.

6. In a die head having a carrier with an enlarged front head providedwith an annular recess in its rear end and substantially radial guideslots for the reception and guidance of thread-cutting chasers having inthe rear transverse grooves within the confines of said annular recessin the carrier head, the combination of an operating member turnable onsaid carrier and having an end face extending to the rear end of saidcarrier head and forming with said radial slots guideways in which saidchasers are fittedly received, said end face being provided with camprojections extending into said annular recess in the carrier head andbeing received in the grooves in said chasers, respectively, for movingthe latter into and from threadcutting engagement with work on turningsaid member in opposite directions within a certain operating range; andyielding detent means on said end face of said member located betweensuccessive cam projections, respectively, and registering with saidguideways only when said cam projections are retracted from the latteron turning said member into a certain position outside said operatingrange, said detent means being arranged yieldingly to engage theopposite side walls of the transverse grooves of said chasers,respectively, to hold said chaser grooves in alignment with the adjacentcam projections for assured entry of the latter into the former onturning said member from said certain position back into said operatingrange.

7. The combination in a die head as set forth in claim 6, in which saiddetent means between each pair of successive cam projections are twospring-urged balls retained in said member and slightly projectingbeyond said end face thereof, said balls being spaced radially of saidcarrier head so that they yieldingly engage the opposite side walls,respectively, of the transverse groove in the adjacent chaser in aradial position of the latter in its guideway in which said transversechaser groove is in alignment with the adjacent retracted cam projectionon said operating member.

8. In a die head having a carrier with substantially radial guidewaysfor thread-cutting chasers, and an operating member turnable on saidcarrier and having cams for moving said guided chasers on turning saidmember, and an annular recess in one end and spaced shoulders within theconfines of said recess, the combination of a retainer member havingfront and rear faces and being releasably mounted with its front face onsaid carrier adjacent said one end of said operating member, saidretainer member having at its front face a projection extending intosaid recess and being provided in its rear face with an annular recess;a helical return spring extending circularly in said recess in theoperating member and being held therein by said retainer member, saidspring being axially compressed and bearing with its ends against saidprojection on said retainer member and one of said shoulders on saidoperating member, respectively, and normally urging the latter into aretract position in which said chasers are retracted from work; amounting member having a flange received in said recess in the retainermember, said mounting member being coupled to said retainer member andnormally yieldingly retained with its flange in said recess in theretainer member, and said retainer member and flange of said mountingmember being provided with aligned apertures having a stop shoulder andsaid flange being provided adjacent said stop shoulder with a peripheralnotch into which said aligned apertures lead and which is exposed at therear face of said flange; a latch pin received with a sliding fit insaid aligned apertures and having a cylindrical shank normally extendinginto said peripheral notch and being within the confines of the latterprovided intermediate its length with opposite flats; a keysubstantially fittedly received in said peripheral notch and having aslot of which a first portion is circular and the remaining portion isstraight and interlocked with said flats on the latch pin shank whensaid key is fittedly received in said peripheral notch; and acompression type spring in said aligned recesses and interposed betweensaid stop shoulder therein and said latch pin to urge the latter intolatching position in which to lock with the other of said shoulders onsaid operating member on turning the latter against the compression ofsaid return spring into an operative position in-which said chasers arein thread-cutting engagement with work, said latch pin being retractedfrom its latching position to release said other shoulder on saidoperating member for spring-return of the latter into said retractposition on yielding separating movement of said retainer and mountingmembers, and said key being removable from interlock with the shank ofsaid latch pin on depressing the latter in said aligned apertures toproject said key outside the confines of said peripheral notch andregistering said circular slot portion in said key with said latch pinshank for axial removal of said key therefrom.

9. The combination in a die head as set forth in claim 8, in which saidlatch pin shank is between said latch pin and said flats and immediatelyadjacent the latter periphorally grooved for the reception of a splitring with which to hold said shank with its fiats outside the confinesof said peripheral groove for interlock of said key with said shank whensaid retainer and mounting members are assembled with each other andwith said carrier.

10. The combination in a die head as set forth in claim 8, in which saidperipheral notch has straight opposite side walls so that the fittedlyreceived key therein will prevent rotation of said latch pin.

References Cited in the file of this patent UNITED STATES PATENTS2,557,040 Strickland June 12, 1951

